Controllable electron discharge tube of the multiple cathode type



June 27,v 1950 Filed Aug. 14, 1947 D. v. EDWARDS El AL 2,512,618 CONTROLLABLE ELECTRON DISCHARGE TUBE OF THE MULTIPLE CATHODE TYPE 3 SheetsSheet 1 FIG.1.

Snnentors 1 DVEdward cirgd DCWin'Len-S Mam Their Gttorneg June 1950 D. v. EDWARDS ET AL 2,512,618

CONTROLLABLE ELECTRON DISCHARGE TUBE OF THE MULTIPLE CATHODE TYPE Filed Aug. 14, 1947 3 Sheets-Sheet 2 Snnentors D.VEdwa.rds and D.C.W|'nters Their (Ittorneg June 27, 1950 D. v. EDWARDS ET AL 2,512,613

CONTROLLABLE ELECTRON DISCHARGE TUBE OF THE MULTIPLE CATHQDE TYPE 3 Sheets-Sheet 5 Filed Aug. 14, 1947 3nnentor's DVEdward-s and D.C.W|'ntera Patented June 27,1950

OONTROLLABLE ELECTRON DISCHARGE TUBE OF THE MULTIPLE CATHODE TYPE Donald v. Edwards, Montclair, and Donald Winters, Newark, N. J., assignors to Electrons, Incorporated, Newark, N. J.,. a corporation of Delaware Application August 14, 1947, Serial N 0. 768,606

19 Claims. (01. 250-275),

This invention relates to electron discharge tubes of the hard vacuum' tube type, and more particularly to triodes used in cross-magnetizing magnetic fields to provide large anode currents without grid losses for use in power amplifiers, oscillators, inverters, and the like.

In one type of hard vacuum triode, such as disclosed for example in our prior application, Ser. No. 726,382, February 4, 1947, conveniently termed a magnatriode, a number of filamentary thermionic emissive cathodes and elongated flat grid bars are disposed alternately in parallel relation between opposing anode surfaces in a strong magnetic field directed transversely of the cathodes, so'that relatively high positive potentials may be applied to the grid bars to obtain large anode currents, without having the substantial electron current to the grid bars and the grid circuit losses characteristic of the conventional triode when operated with positive grid potentials.

The primary object of the present invention is to provide a tube structure of this magnatriode type, in which suitable areas for cathode emission and grid control for large anode currents may be obtained within over-all dimensions suitable for use in an efficient magnetic circuit, and in which the desired relatively close spaced relationship of the parts, with the necessary electrical isolation or insulation between the parts, may be readily obtained, and maintained under operating conditions of temperature and the like, in a simple structure easily fabricated and assembled.

Various other objects, attributes, and advantages of the invention will be in part apparent, and in part pointed out as the description progresses.

Generally speaking by way of explanation, and without attempting to define the nature and scope of the invention, it is proposed to support the ends of the grid bars and cathodes in such a type of tube by headers of steatite or like heat resistant insulating material, with adequate provision for allowing endwise expansion of these grid bars and cathodes under changes in temperature, and to utilize the anode for supporting and maintaining the headers and associated grid bars and cathodes in the proper space relation. It should be understood that various adaptations, modifications and additions may be made to the structural organization thus outlined in this explanatory statement without departing from the invention.

In the accompanying drawings, which illustrate one specific embodiment of the invention, Fig. 1 is a general view showing in outline one typical application of the tube structure of this invention using a permanent magnet for providing the cross-magnetizing field.

Fig. 2 illustrates schematically for explanatory purposes atransverse section through what may be termed an elemental unit of the magnatriode type of tube, which constitutes the basis of the tube structure of this invention.

Fig. 3 is one view of the general organization of the tube of this invention, in the form of a longitudinal section through the tube, with part of the anode removed.

Fig. 4 is another longitudinal section through the tube in another plane along the line indicated at 4 -4 in Fig. 3.

Figs. 5 and 6 are two transverse sections through the tube along the lines 5-5 and 6-6 respectively in Fig. 3.

Figs. 7, 8 and 9 are fragmentary enlarged views illustrating certain details of the mounting end support for the cathodes and grid bars characteristic of this invention.

Before describing in detail the particular embodiment of the invention shown, it would appear to be expedient to outline briefly the purposes and functions of this magnatriode type of tube, and some of the problems involved in providing a suitable tube structure of this kind. For this purpose there is shown schematically in Fig. 2 a transverse section through the cathode, grid bars and anodes of what may be termed an elemental unit of this type of tube, which is developed or expanded in the tube structure of this invention. Referring to Fig. 2, the thermionic emissive cathode C is of the elongated or filamentary type, and is disposed between and at substantially equal distances from two anodes or plates A and A and two fiat grid bars G and G in the manner indicated in Fig. 2. The cathode C, grid bars G, G and anodes A, A which are shown in cross section in Fig. 2, are assumed to be extended to an appropriate length. This arrangement of tube elements, enclosed within a suitable evacuated envelope (not shown in Fig. 2) is disposed in astrong uni-directional magnetic field between the pole pieces designated N and S of a permanent magnet, or equivalent source of magneto-motive-force. The magnetic lines of force through the tube act in the direction indicated by the arrow I-I substantially at right angles to the surfaces of the anodes A, A and parallel with the surfaces of the grid bars G, G

In-this elemental magnatrlode unit shown in Fig. 2, it can be seen that the potential on the grid bars G, G} will act to control or modify the potential gradient to the emissive surface of the cathode C as provided by the space charge and anode voltage, and thus govern the anode current in much the same way as if the grid were located in the direct path for electron movement from the cathode to the anode, as in the conventional triode. The magnetic field acting in the direction indicated by the arrow H, and constituting a cross-magnetizing, field with respect to the cathode C, may be said to act, in accordance with well known principles relating to the movement of electrons in a magnetic field, to converge or focus the electrons leaving the cathode C into beams or streams, such as indicated by dotted lines 5 in Fig. 2. Assuming the appropriate strength of magnetic field with respect to the spacing of the tube elements and voltages involved, a relatively high positive potential may be applied to the grid bars G, G to neutralize the space charge and obtain large anode currents, without having appreciable electron current to these grid bars, since the eifect of the magnetic field is to confine the electrons coming from the cathode to paths which do not touch the grid bars. This and other operating characteristics of the magnatriode type of tube, as exemplified in the elemental unit shown in Fig. 2, enable such a tube to be advantageously employed in various types of circuit organizations suitable for conventional triodes, such as amplifiers, oscillators,

control rectifiers, inverters and the like; but since such applications and uses of this type of tube are not material to the present invention and form the subject matter of other applications, it is unnecessary to discuss further the operating characteristics and advantages of the magnatriode type of tube. Also, this type of tube is disclosed and claimed in other applications, such as our prior application above mentioned; and no claim is made herein to the basic features, functions and structures disclosed in these other applications.

Generally speaking, the tube structure of this invention involves a unitary assembly of a number of elemental tube units shown in Fig. 2 side by side, in such a manner as to establish and maintain under operating conditions the desirable relatively'close space relation between the tube elements in an isolated or insulated relation. In providing such a tube structure, among other things it is desirable to provide a compact assemblage within over-all dimensions suitable for disposition of the tube in a short airgap of a magnetic circuit, so that a strong magnetic field through the tube is obtained for the size of permanent magnet or equivalent source of magneto-motive-force employed. During operation of the tube the various parts of such a compact assembly tend to assume high and somewhat variable temperatures; and in supporting cathodes and grid bars in their relatively close relationship to each other and the anode surfaces, it is necessary to make provision for their expansion under changes of temperature without materially disturbing this space relationship. Also, in this type of tube, the heating current through the cathodes creates a magnetic field which reacts with the strong magnetic field in which the tube is disposed in a way to exert a sidewise bending or displacing force upon the cathode, as later described; and in order to limit the effects of such motor action, it is desirable to provide, in addition to using a cross section for the cathodes suitable for resisting such bending force, a form of support for these cathodes which 4 will exert an endwise pull thereon when heated. The structural organization characteristic of this invention satisfies these and other requirements or conditions for the magnatriode type of tube in a simple and efiective manner.

Considering now the specific embodiment of the invention illustrated in the accompanying drawings, it is assumed that the tube will be disposed in the airgap of a. permanent magnet; and as atypical example of such an application of the tube, Fig. 1 shows in outline a tube T in connection with one form of a permanent magnet. In the particular arrangement shown, which of course is merely typical and is susceptible to various modifications, the permanent magnet comprises two curved arms 6, assumed to be circular in cross section, formed of a permanent magnet material, such as the alloy commonly known as Alnico. The lower ends of these curved arms 6 are attached to a soft iron back yoke or base ain a suitable manner, such as by screws (not shown) threaded into inserts in the ends of these arms. Soft iron pole pieces 8 of a general rectangular shape are fastened in a similar manner to the upper ends of the arms 6 of the permanent magnet, these pole pieces being parallel and providing an airgap as small as the dimensions of the tube T will permit. The grid bars and anode are disposed in the envelope of the tube T, so that when the tube T is. in place, as shown in Fig. 1, the magnetic lines of force act in a direction with relation to these grid bars and anode, asv indicated in Fig. 2. As illustrated in Fig. 1, it is assumed that the tube T will be supported in an upright position by a suitable base and socket, generally indicated in outline at 9, mounted on the back yoke l of the magnet. The arrangement shown in Fig. l is merely representative of the various ways in which the tube structure of this invention may be associated with a magnetic circuit; and it is contemplated that. various expedients in the way of forced draft air cooling or immersion in oil may be employed for heat dissipation as required.

'In order that the tube may be employed in the short airgap of an efiicient magnetic circuit, such as between the pole pieces of the permanent magnet in Fig. 1, it is desirable that the tube should be relatively thin or narrow in thickness to fit in a short airgap between such pole pieces, which may be enlarged to cover the length of the tube appropriate to the strength of the filamentary cathode and a width conforming with the number and spacing of grid bars being employed in the particular tube structure. Accordingly, the tube elements are arranged and disposed within a tube envelope which is relatively thin in thickness as compared with its breadth and width. In the embodiment of the invention shown, this tube envelope E is assumed to be of glass, and to have walls which are straight longitudinally of the tube, but curved transversely to have a general elliptical cross section, as shown in Figs. 5 and 6, so that the walls of this. envelope will have the necessary strength to resist pressure when exhausted. The tube elementsare supported in a press l2 formed at the lower end of the envelope E in the usual manner; and the envelope is provided with a tubulation, at the other end, such as indicated at P3, iorexhaust purposes.

The assembly of tube elements comprises a number of narrow elongated grid bars G in substantially equally spaced parallel relation and filamentary cathodes C arranged alternately in posed edgewise to opposing anode surfaces.

- steatite.

'aimulticellulanboxelike assembly, which is located .inside :of a hollow sheet metal anode A of rectangularicross section, with the grid bars dis- The typical arrangement shown comprises seven grid bars G and sixcathodes C.

The anode A is formed from sheet stock of a suitable non-magnetic material, such as tantalum, molybdenum, or the like, in two halves having flanges [5 which are welded together as shown in Fig. 5, so as to form a hollow box or tube of rectangular cross section. This anode A is supported by two rods I6 welded to its narrow sides which are anchored to lead-in supports H extending through seals in the press I2 of the envelope, to constitute a rigid support for the anode A and also provideiexternal connections for the anode circuit. The anode A is slotted or notched near the corners at both ends, so that edge portions along the ends of the wide sides may be bent in slightly, as shown in Fig. 4, to con- ;.;ported at their ends by upper and lower supporting elements or headers 2|, 22 of a heat resistant insulating material,preferably one of the ceramic materials, such as commonly known as These headers have a cross section, such as indicated in Fig. 7, to have the necessary lateral stiffness and have a ledge or shoulder 24 along their longitudinal edges to be engaged by the bent-in edges or lips IQ of 1 the anode. The same header as shown in Fig. 7 for the upper end of the tube is turned upside down for the lower header 22. In other'words, the insulator headers 2|, 22 are held apartin a predetermined space relation by the engagement of the lips l9 at the .ends of the anode A with the shoulders 24 on these headers.

The upper and lower headers 2|, 22. are each formed with transverse slots 25 to receive the ends of the grid bars G, as shown in Figs. 7 and 8. These grid bars G are flat, narrow, elongated strips and are fitted into the slots 25 of the headers 2i, 22 with a small clearance to prevent binding, but permitting endwise movement of these grid bars when expanded lengthwise under temperature changes. The grid bars G are held in place in the upper header 2! after assembly by a small rod or wire 26 welded to one edge of these grid bars and resting on a ledge of the insulator header, as shown in Figs. 4 and '7. The grid bars G at their lower ends have a similar rod 21 welded to their edges (see Fig. 3), which in turn is bent and welded to a grid lead-in support 28, sealed in the press l2 of the envelope, to afford an external electrical connection to the grid bars G, as can be readily understood.

The grid bars G are preferably of such a length that they do not extend the full depth of the slots 25 in the insulator headers, 2|, 22; and these slots 25 are also preferably made somewhat wider,

for a portion of their depth than the thickness of these grid bars, as best shown inFig. 8, so that .theslots afford additionalsurfaces to increase .the distance'for surface leakage over the insu- .lator headers b tween the grid bar and, the a jacent cathodes, which are disposed: between thesegrid bars'in a manner later. described: Also, the vertical'portions ofusuch leakage surface adjacent a grid bar are closely spaced thereto, so as .to. be shielded from condensation of evaporated materials'comi-ng from the cathodes and other tube elements during the out-gassing and exhaust procedure. A similar protected creepage surfaceis provided for each of the cathodes, as later pointed. out.-, In this connection, it can be appreciated that the accumulation of, evaporants surfaces of these insulators from condensation of evaporants.

-The grid bars Gare made of a non-magnetic metal suitable for use inhardvacuumtubes-at the temperature involved. Tantalum. molybdenum, Nichromeand similar metals are generally suitable for this purpose; and for some types of tubes, itis desirable to provide surface oxidation or. other. surface treatment for the grid bars G to reduce their tendency to become emissive at the temperatures they acquire in thecompact -as sembly characteristic of this invention for tubes of the higher ratings. M,

The cathodes C are of theelongated or-filamentary form, andmay be tungsten, thoriated tungsten, or of the oxidencoated" type, as best suited for the rating and operating requirements of the tube.- As shown in Figs. 3 to 9 it;is assumed that the cathodes Cv comprise anickel tube 3! as a core (see Figs. '7 and 8) and have formed thereon an oxide coating, indicated in an exaggerated manner at 32, which may be formed in accordance with the disclosure of the priorpatent to D. V. Edwards et al., No. 1,985,855, dated December 25-,.1934. A tube of circular. or oval cross sec- :tion represents a simple and convenient way of providinga distribution of metal for the cathodes in across section adapted to resist the sidewise bendingforce of what may be termed motor ac- ,tion characteristic of this type of tube. Considering this motor action effect, and'referring .to

-indicatedby the arrow H, in one directionor the motor action tends tovarythe distance between the grid bars and the cathode for different parts of its;length, and thus interfere with the: control .and operating characteristics of the tube. Also,

if alternating current is used for heating ,the cathode C, as-is usually most convenient, this .motor action tends to vibrate .the cathodeand cause failure on account of metal fatigue. Consequently, it is desirablepto employ a, cross section for the cathode, such as the tubular arrangement assumed, which will resistpto the best ad- Ttubular cathode-ins illustrated in: Figs. 7 and ffiiis rmerely typical and:- it is:-'contemplated z-thatoxide "coated icathoides of :other cross sections, such as channel shaped, rectangular, or-the like, maybe employed. '.:Further,' thecathode may"=be:a:-strip i34 of j-tungsten .or thoriated tungsten dispose'd *edgewise Ito the grid bars '.-G, as: indicatedinf the modification-ofiFig. '9. When a: stripofi tungsten is used, as in themodification of :FigJiS; it is 'prefenable to v.p'rovide an end connector-of good he'at conductivity, such as indicated at:"35--inFig.19,.to which :the tungsten strip fl is welded, since the :emission temperature for tungsten is high :as compared: with-what theainsulator Zhea'ders Z I [2-2 are adapted to withstand a'nd it is desirable "to -use 'aconnector.operatingiata lower temperature ier-direct contaet with these -insulator =headcrs.

The ca'thodes C, in :a spaced -parallel relatio'n ito the grid bars 'G, as shown in Figs. 3 and= 5g are supported by the upper and lower insulator'headers -ll '22 im a man ner' 'to I permit :erfdwise expan- -'sion of the cathodesgand preferably with means "for exerting an :endwise pu1l= on these .icathoches indivi'dually after they :are heated. In' theparticular construction illustrated, the mathodes at their upper-ends extend with a-close but s'lidable fit through spaced holes 38 in' the upper -header 2i said holes being preferably enlarged "for a portion of their "length, as best shown in E'Figj 8, to increase the I distance I for 'surface leakage between each cathode and theadjacent -grid bars. The extreme upper end portions of the -cathodes C 'are flattene'd and extend through holes in a somewhat flexible 1 cross member or :plate 39 and :each i cathode i is attached to this plate by a: small angle :bracket 'k'fl -welded to the flattened end :portion i'Of the 'cathode and the -cro'ss member 39; A resilient-element, in the form of a compressio'n coil spring around each end "of the cathode is interposed be'tween the cross memberailsgto which the cathodes a're attached, -an'd theitop of the upper header 2 I. l hese springs fl may beimade' of tungsten,molybdenum, orlsimilar =material, and after being :loos'ely wound 1 in a spiral, are preferably subjected -to a-preliminary baking and writ-gassing iproce'dure in wacuum, after-which they are compressed to prov-ide the appropriate tensio'nprior to assembly in the tube. springsof'other suitable materialyor other forms of-resilient elements may be used.

#The lower en'ds *of the cathodes C extend through 'spa'ce'd holes the bottom "insulator "header -ZZpand half of the oathodes, three as shown, have =their :end 1 portions flattened hand wvelded to one a cross bar 45 attached to a cathode "support and lead-in rod 46 sealed in 'the press F2 in the envelope and the other halfof these cathodes are welded in --a similar manner to anothencross barifll :attached' itoza sim ilar cathode support-and lead-m ro'df'48. -Et cambe-seen that the"heating current suppliedto" the cathode lea'd in rods 46, 58 will flow in one direction throughi-three *of the "cathodes in multiple td'the atop of cross'member -39,-:and in the other direction through theother :three :cathodes in multiple.

V arious procedures '=n-iay *be followed "for assembly of this tube structure. 'Foroxide-coated oathed-es, such as assumed for -the structure shown in FigsQ 3 -to:8,-it is pre'ferableto assemble-the -nickel tubes 31 for these-cathodes in -the w insulator headers l I 22 wh'ile heldapart in the 'proper space i relation by some =suitable detach- "aible spacing clamp, apply treat the oxide coatinggand F then insert the grid bars GT in -the one 25 in the -insulator heaiders '2 l 22 1mm the bottom, melding :the 'rods or wires 26, :21 tto ithe edges o'f the'se :gri'd bars to rhold 'ithem zin .place. After this partialiassembly, the: anode-nz-isr substituted for the II temporary spa'cing :device ':being used. The complete assembly may then be :in-

serted in the envelope E, andthe -press 12 formed inithe regular -way to hold the assembly of i tube elements imposition.

It is -assumed that, after the tube elements have i been mounted in the 1 envelope, *the appro- -priate *procedure' will be followed to -activate the cathodes and thoroughly out-gas all o'fthe parts, --connecting='-theenvelope E to the vaeuum system 'by the'tubulation 1' 3 duringthisoperation. N0 unusual'or special exhaust or :out-gassing pro- -cedure is'require'd forthe tube structure'of this invention, other than employed for "ordinaryhard vacuum tubes in accordance *with "established practice. It is'coritemplatetl that-the envelope "Will be fully'exhausted toeliminate as far-as practicalalltraces of air-orgas. It is-gener-ally preferable-to use metals such as molybdenum, tantalum, tungsten -01 perhaps N-ichrom'e 'for the various tube elements and supports, *on account oftheir non-magnetic qualities *needed to avoid distortion of the magnetic field characteristic of this type of tube. -It shouldbe understood, "however, that there considerableohoioe in the materials that can be used-successfully :for the electrodes, supporting-elements and insu'lators of thetube structureof this invention; and; itis not intended-to limit this invention to-any' particular type or combination of materials.

Froni'the foregoing-it can be appreciated that the organizatiomor' assembly of I parts characteristic of this invention provides acompactunitary assembly ofthe componentelements'for a tubeof *this 'type in the appropriate over-all dimensions and with such relatively close spacing o'f cath- -'odes, grid bars and anodes,=*as "may be desirable for certain Y tube characteristics. "-The grid bars G -may expand endwise when heated "without being Warpedorbent. The cathodec are somounte'd that they 5 may reaIdily expand lengthwise when -heated; and in -aiidition tohaving a cross scotion suitable :for'resisting the force of motor action characteristic of this type of tube,are=s-ubfretted-"to an ei-idwise tension orpull,'-Wh-ich-keeps 'these cathodes straight and-in the' properspace relationfto the gri'd =barsand= anodes, and tends to prevent si'dewise' bending or displacement-of the cathodes by any twisting-or warping'action' of the force ofz motor action, I that might otherwise with the limited amount of metal available :for the cross seotionxof the cathode permit such -ben'ding distortion. 'J'Jhe'anode A itself supports .the i insulator headers -21, 22 carrying the g'ri'd bars and cathodes, thereby providing =a=-predeter-mir-ied relationship between :the parts inde- :pendently of the means supportingthe-tube ele- "ments in the envelope. Incidentally, -the endwise' expansion: of theranode A when heated'com- -pensates-to some extent for the expansion of the grid 'bars and cathodes. The insulator headers 2 [522 are disposed largely outside of the ano'deA, and hence, together with-the springs 42 'Wholly outside of'the anode A,-tend-to assume a-low'temperature as com-pared with the other parts enclosed-within the anode.

Obviously, the same general organization shown may-be -employed to provide as iew or "as many of "the elemental-tube units of Fig-'2 ---as may -"-be expedient. -'Inthis connection, I the spacing be- "tween the gri'd barsG and -the cathodes C is determined 'by the insulator 'l ieaders 2 I, 22; and

since these headers aremade of steatite or equivalent insulating material, which does not expand materially with changes in temperature, a relatively large number of gridbars and cathodes may be employed, without causing their space relationship to be changed by expansion under operating temperatures, as in the case where metallic elementsare used tosupport the ends of the grid bars and cathodes and determine their space relation. I i

The specific tube structure shown and described will serve to illustrate the nature of the invention as exemplified in one specific embodiment; but it should be understood that various adaptations, modifications, and additions may be made 'to the particular structure illustrated without departing from the invention.

What we claim'isi a 1. 'An electron discharge tube for use in a cross-magnetizing field comprising in com-bination with an envelope having substantial breadth and width with respect to its thickness for disposition in the short airgap of a magnetic circuit, a multicellular assemblage of grid bars and'filamentary cathodesarranged alternatelyin' parallel relation between opposing parallel anode surfaces, said grid bars being disposed edgewise to said opposing flat surfaces of the anodefmeans including insulators of ceramic material supporting said grid bars and cathodes wholly from said anode in a predetermined spacerelation to each other and to said anode surfaces, and means supporting said assembly of grid bars, cathodes and anode in said envelope." r

2. An electron discharge tube for usein acrossmagnetizing field comprising in combination, a pair of narrow elongated headers of heat re-' sistant insulating material, a plurality" of: narrow elongated grid bars slidably supported at their ends in spaced slotsin said headers, a plurality of filamentary thermionic emissive cathodes "sup ported by said headers in parallel relation with said grid bars, one cathode between each pair "of grid bars, and ,an elongated hollow sheet metal anode around said grid bars and cathodes, said headers of insulating material being supported and held apart in a predetermined space relation wholly by said anode.

3. A hard vacuum triode comprising in combi nation, an envelope relatively long and wide with respect to its thickness, and a unitary multicellular assembly of alternate elongated grid bars and filamentary cathodes in parallel relation between opposing flat anode surfaces disposed in said envelope, said assembly including headers of heat resistant insulating material wholly supported by the anode for supporting the grid bars and cathodes and for permitting endwise expansion thereof individually.

4. An electron discharge tube comprising in combination, a plurality of narrow elongated flat grid bars and filamentary thermionic emissive cathodes disposed alternately in parallel relation, a pair of long headers of insulating and heat resistant material supporting said grid bars and cathodes at their ends and permitting endwise expansion individually, and an anode outside said grid bars and cathodes and including opposing fiat surfaces in planes substantially at right angles to the planes of said grid bars, said anode supporting said headers in a predetermined spaced relation to each other and tosaid anode.

5. An electron discharge tube comprising in combination, a hollow sheet metal anode of rectangular cross section, a pair of spaced headers of ceramic" material supportedby said anode" at its ends, and a plurality of elongated grid b'arsand filamentary cathodes arranged alternately in parallel relatiodand' wholly supported "by said headers, said headers supporting saidgrid bars and cathodes to permit individual endwise expansion thereof while insulating them from each other and from the anode.

-6. An electron discharge tube comprising in combination, an'envelope of substantial lbreadth andwidth with respect to its thickness, an anode having two opposing spaced parallel surfaces supported within said envelope, a multicellular assembly of elongated fiat grid bars and filainentary cathodes disposed alternately in parallel relation between the opposing surfaces of said anode, said grids being in planes essentially at right angles to the planes of said anode surfaces, and' 'means including blocks of ceramic insulating material wholly supported by said anode for supporting said grid bars and cathodes in a predetermined space relationship to each other and to said anode surfaces.

7. A controllable electron discharge tube structure, comprising in combination with a pair of supporting headers of a ceramic insulating material,- a plurality of filamentary thermionic emissive cathodes supported at their ends by said headers in a spaced parallel relation in a common plane, and means associated with said cathodes and said headers for permitting individual endwise expansion of said cathodes with respect to said headers and formalntaining an endwise pull on said cathodes'individually after being heated 1' under the operating conditions for the tube.

8. Ahard vacuum tube comprising, in combination with an-anode having two fiat walls in spaced parallel'relation, a pair of blocks of a ceramic insulating material at the ends of said anode walls and wholly supported thereby, a plurality of alternately arranged elongated fiat grid bars and filamentary cathodes between said anode walls, said grid bars and cathodes being supported by-said insulating blocks in a substantially equally spaced parallel relation, means electrically connecting said grid bars together, and means electrically connecting said cathodes for flow-of heating current therein" in opposite directions. l i

9. An electron discharge tube for use in a crossmagneti'zing field comprising in combination, a tubular sheet metal anode of a substantially rectangular cross section, a pair of headers of "a ceramic insulating material wholly supported by the ends of said anode, and a multicellular assembly of alternate elongated flat grid [bars and filamentary cathodes supported by said headers within said anode, said grid bars being disposed in planes substantially at right angles to opposing surfaces of the anode.

10. An electron discharge tube structure comprising in combination, an anode having parallel opposing surfaces, insulator headers of steatite wholly supported by said anode, a plurality of elongated flat grid bars supported for endwise sliding movement in slots in said headers, said grid bars being disposed edgewise to said anode surfaces, and a plurality of filamentary thermionic emissive cathodes supported by said headers one between each adjacent pair of grid bars.

11. A hard vacuum triode for use in a crossmagnetizing field comprising in combination, a pair of headers of rigid insulating material having substantially equally spaced slots and holes therein, a plurality of narrow elongated grid bars slidably supported at their ends in the slots f said headers, a plurality of filamentary thermionic emissive cathodes supported in saidholes of said headers between said grid ibars, and anode having opposing surfaces opposite the edges of said grid bars for supportin and maintaining said headers in a predetermined space relation.

l2. A cathode structure ffOI a hard vacuum triode comprising :in combination, a pair of spaced blocks of ceramic material constituting cathode headers and having a plurality of spaced holes therein, a plurality of :filamentary thermionic emissive cathodes disposed in essentially equally spaced parallel relation in a common plane, said cathodes extending at their ends through said holes, means electrically connect n 3 3 of s id cathodes together to one end, and separate means electrically connecting together different groups of said cathodes at the other end, whereby the heating current passes in one direction through one group of cathodes and in the opposite direction through the other group.

13,. A hard vacuum triode comprising in .combination with a plurality of narrow elongated fiat grid bars, of -a pair of supporting headers for supporting said grid bars at their ends in equal-l5, spaced parallel relation, said headers being of a ceramic insulating material and having spaced slots therein to slida-bly receive the ends of 'said grid bars.

14. A grid supporting structure for electron discharge tubes comprising incombina-t-ion, a pair of blocks of ceramic heat resistant material having equally spaced slots therein, a plurality or elongated grid :bars slidably fitting at their e in said slots, and means welded to the ed es ct said grid bars for electrically connecting them and holding them together in place in the slots of said :blocks.

'15. A cathode structure for electron discharge tubes comprising in combination, a pair of insulator headers of a rigid heat resistant insulating material having spaced holes therein, a plurality of filamentary cathodes extending at th ir 1 ends through said holes, and individual refiilient elements for said cathodes cooperating with one of said headers to exert an endwise pull on the corresponding cathode when heated.

1.6. .A controllable electron dis arge tube st u ture com-prising, in combination with a plurality of filamentary cathodes disposed in aspaced parallel relation in a common plane, a pair of insulator headers of a rigid heat resistance insulating material having spaced holes therein, said oath-- odes extending at their ends through the holes in said headers, and means including a flexible member for electrically connecting said cathodes together at one end.

17. An electron discharge tube comprising, in combination with an insulator header of ceramic material having a plurality of equally spaced holes therein in a common plane, a plurality of cathodes extending at their ends through said header, said cathodes having a cross-section resisting sidewise bending in parallel planes, and means including resilient elements cooperating with said header for electrically connecting said cathodes together and exerting an endwise pull on said cathodes.

18. A cathode structure for electron discharge tubes comprising in combination, a block of heat resistant insulating material of a ceramic nature constituting a cathode supporting element and having a plurality of eq-uallyspaced holes therein in .a common plane, a plurality of filamentary cathod s extending at their ends through said holes in said header, a flexible-cross member connected to the ends .of said cathodes, and a resilient element for each cathode interposed between said header and said cross member.

.19, An electrode assembly for hard vacuum electron discharge tubes comprising in combination, a pair of headers of insulating and heat resistant material, and a plurality of elongated grid bars and filamentary cathodes arranged alternately in parallel relation, each of said headers having therein a, row of substantially equally spaced openings to receive the ends of REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Ekstrand et a1. Dec. 23, 1-941 Number 

